1、*.,/-.4o1?a:NAIONALADVISORYCOMMITTEEFOR AERONAUTICSTECHNICAL NOTE 4172NOISE SURVEY UNOER STATIC CONDITIONS OF ATURBINE-DRIVEN FULL-SCALE MODIFIEDSUPERSONIC PROPELLER WITH ANADVANCE RATIO OF 3.2By Max C . KurbjunLangley Aeronautical LaboratoryLangley Field, Va.WashingtonJU211y 1958Provided by IHSNot
2、for ResaleNo reproduction or networking permitted without license from IHS-,-,-TECH LIBRARY KAFB, NMlG NATIONAL KDVISORY COMMITTEETECENICAL WIT 4172NOISE SURVEY UNDER STATIC CONDITIONS OF ATURBINE-DRIVENFULL-SCALE MODIFIEDSUPERSONIC PROPEILER W13!HANLOVANCE RATIO OF 3.2Max C. Karb$msuMMmYOverall sou
3、nd-pressurelevels and frequency spectra have beenobtained under static conditions from a mcdified supersonicpropellerdesigned to operate efficiently at a high forward speed without the highnoise levels associatedwith the supersonicpropeller. The three-blade,lo-foot-diameter,1,700-rpm propemg iS pmer
4、ed by a tbe enne =dis designed to operate at a Wch number of 0.95 at 40,000 feet.The results consist of overall sound-pressurelevels and frequencyspectra obtained from analyses made of recordings taken during groundrumps of the modified supersonicpropeller. These results are cmparedwith sitilar resu
5、lts obtainedwith a conventional subsonicpropellerreported in NACA Technical Note 3422 and with a supersonicpropellerreported in NACA Technical Note 4059.The noise output of the modified supersonicpropeller displaysapproximatelythe same overall sound-pressurelevel and frequency-spectrumcharacteristic
6、s,under static conditions as the cment subsonictransport propeller reported in NACA Technical Note 3422. The maximumoverall sound-pressurelevel produced was 120 decibels at a distance of100 feet. This overall noise output represents a lowering of the maxi-mum overall sound-pressurelevels by approxim
7、ately10 decibels at com-parable engine horsepowers as comparedwith the output of the supersonicpropeller reported in NACA Technical Note 4059. In general, it III the equipment vsried #from that used in references 1 snd 2 in that an Altec-Lansingmodel M-1bmicrophone system incorporatinga 21BK150micro
8、phone was used.Sound recordingswere taken at various azimuth-anglestations,on the ground, around a circlewith a 100-footradius about the pro-peller hub. The location selected for the sound measurementswas a com-crete apron with no buildings or other large reflective surfaceswithin300 yards.The radia
9、l distributionwas made during one continuousengine test,in which the power settingwas 1,050 hpand the propeller speed was1,675 rpm-: The engine operating conditionswere varied during theinvestigationto enable sound recordingsto be made at station 105 toshow the effects of propeller rotational speed
10、and power. The test con-ditions and results of the noise analysis are presented in table II.=b“.The calibrationof the noise recording and analyzing equipmentwasperformed essentiallyin the sane manner as that described in refer-ence 1. Other pertinent informationis as-follows:Clearance of ground by p
11、ropeller, ft . . . . . . . . . . . . . . 1.0WlndfromOOtonose, hots . . . . . . . . . . . . . . . . . . 4Temperature, % . . . . . . . . . . . . . . . . . . . . . . . . 65Barometricpressure, in. Hg . . . . . . . . . . . . . . . . . . 30.1RESULTS AND DISCUSSIONThe modified supersonicpropeller usedin th
12、e present investigationis one of a series of propeller designs to be tested in the propellerflight research program of the NationalAdtisory C-6mmitteefor Aero-nautics. Thus far, three propeller designs have undergone noise investi-gations. The relation of these three propellersmakes it desirabletopr
13、esent some of the results of the first two propeller designs investi-gated (refs. 1 and 2) and to compare theseresults with those of the pres-ent investigation. The-propellerof reference 1 is a conventionaltypeand differs mainly from the present modified supersonicpropeller in thatthe blades have hi
14、gher thickness ratios and it is a four-blade configu-ration. The propeller of reference 2 is a supersonicpropeller with thesame design conditionsof the present propeller except for a loweradvance ratio. The measurementsof references 1 and 2 have been adjustedfor differences in power and distance to
15、agree with the measurementsofthe present investigation. .-=hProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 4172 5Distribution of Overall Sound-Ressure Levels.The radial distributions of the overall sound-pressurelevels ofv the three propelle
16、rs are shown in figure 4. The maximum overall sound-pressure level for the modified supersonicpropeller is seen to be120 decibels in the right resr quadrant of the propeller plane. Thisvalue is approximately 10 decibels lower than the maximum overall noise “level produced by the supersonicpropeller.
17、 Also, a slight shift in theorientation of the maximum level station is noted.The comparison shows that the nmdified supersonicpropeller producesnoise levels only a few decibels higher than those of the subsonic pro-peller; however, several pyopeller parameters differ in the comparison.The first par
18、ameter, the number of blades, is probably the cause of thelower measured sound-pressurelevels of the subsonic propeller. Thesecond parsmeter, the thickness of the propeller blades, is not expectedto influencethe noise output under static conditions. At flight speeds,however, noise due to thiclmess m
19、ay increase to an appreciable extentas is suggestedby the theory of reference 3 and by the results of thetests conducted in reference 4.The agreement of the overall sound-pressurelevels of the modifiedsupersonicpropeller with those of the subsonic propeller and the agree-ment shown in reference 1 be
20、tween the calculated overall.levels by the. theory of reference 5 and the measured levels of the subsonicpropellerimplies that the theory will also apply eqly well for the presentmodified supersonicpropeller. A complete comparison of the theory and. test results of the subsonic propeller is made in
21、reference 1.The modified supersonicpropeller shows an unsymmetrical distri-bution of overall noise similar to that of the subsonicpropeller, thehighest level (120 decibels) being in the right rear quadrant. Thesupersonicpropeller displayed an unsymmetrical distributionbut to alesser deee. As mention
22、ed in reference 2, the difference in distri-bution is believed to be due in part to the differences in gyoundclearances affecting the inflow to the propellers.Variation of Sound-PressureLevel With Freq.cyThe frequency spectrum of each of the three propellers is plottedin figure 5 for station 105. Th
23、e spectrum of the modified-supersonicpropeller is seen to be very near the same as that of the subsonic pro-peller with a rapid dropoff in sound-pressurelevel at the higher har-monics. The supersonicpropeller displays high noise levels in thehigher harmonicswhich are usually displayedby a high-tip-s
24、peed.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6 NhCA TN 4172propeller. At this station the superswic propeller produces 9 decibelshigher overall sound-pressurelevel than does the modified supersonic 120.o 119.5113.0UO.5 l.w,1o5.5 91-.OI.9l(x.o
25、m % L 050 M 83.5 LLq.0 lW.O s.5 llxl.5K13.51.07.51.07.o103.0 y(.oPolaraistributiom255 %540 L 030 E?J.5Cnne.tantIJ$.0 m .0K6.y W5.o S-9.5n .0 95.0 .0 g5.o w-warmnditica,mMmcms270 2,340L WQ J-6 m.5 IJb.5 IIQ.gmoo m? .51.02.5913JJg1(%.0IJ6.ol135.51.%.51m.olvariawm ofpwnr: l,o l.pm% %: %: !3:;93.7 55.5
26、93.5 $2.0.I. uProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-, , ,1 II,1 !il,!1L-96377Elgm?e l.- Modifled supersonicpropellexmounted on test airplane.i%!2Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,
27、-,-12.25.20.15b/D. 0.050h/b.06.05.04.03.02,018(6CP,deg5(4C3C_-J-H+ II/-B, de9spinner junctureI.6curves of modified supersonicpresent investigation.8propeller1.0used in.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-, r . *General radio sound-level c
28、alibratorH rr”icrophoneP “”fine-i:T 3-blade Subsonic propeller; 4-blade21(Y 200” 190” 180” 1709 16(P 150”.Figure 4.- Overall sound-pressurelevels for three propellers at ,100-foot dis-ce. P = 1,050 hp.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N
29、ACA 15-,12812412C116112KM10410096OverRjI I I /1I If r ,4 / “ NAG Supersonic propeller (ref. 2) 2 Q Subsonic propeller (ref. 1)Modified supersonic propelleri?)692,02 4 6 fFrequency, cps10 1Ieve!sEl-”oo-I4 XI02Figure 5 Comparison of overall sound-pressurelevels and frequencyspectra of three propellers
30、. Station 105; 100-foot distance;P = l,t)50 hp.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-16 NACA TN 4172125P, hpo 1,050 Overall levels 350120 8-=- 150 n115a75 . -110 m n“e -nu_.w100-foot distance. .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3Ga71a13.TN 417211:foIoz10(120116Overall levelsc1n EL bb 1,675 rpm, P= 154)hp, T=670 lb , M+.0.7 100-foot distance.NACA - LangIey Flew Va.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
